Conventionally, for a flexure used for a suspension for a hard disc, a polyimide metal laminate mainly comprising copper alloy/polyimide/SUS304 is used. Particularly, according to capacity increase and densification in a hard disc in recent years, an amount of suspension use is increasing. Therefore, in order to improve production efficiency, suspension processing makers have endeavored to achieve a high efficiency in each manufacturing step.
However, in case that the above-described polyimide metal laminate is used, there occurs such a problem that, in a step that polyimide is etched after SUS 304 developing a suspension function has been etched with aqueous solution of ferric oxide, when a polyimide etching is performed, an etching rate varies for each lot of SUS304. For this reason, in order to realize a secure polyimide etching, a polyimide etching over a long term is required, which prevents a high efficiency from being attained.
As etching of polyimide, there are a method employing a dry etching where etching is conducted using plasma gas such as NF3, SF6 or the like (refer to JP2002-25027A) and a method employing a wet etching where strong alkaline solution such as hydrazine solution, potassium hydroxide solution or the like (JP2001-55570A). Even in case that either one of the etching methods is used, an etching rate of polyimide coming in contact with SUS304 varies according to respective lots of SUS304 to be used. For this reason, in order to conduct polyimide etching completely, it is necessary to set an etching time to be long so as to meet a case that the etching rate is slow. In such a polyimide etching over a long time, a phenomenon where polyimide is etched excessively over a predetermined size, so-called over-etching phenomenon is observed. Therefore, not only a problem that the above-described long time etching is required occurs but also there occurs a problem in etching shape.
As an example where wet-etchable polyimide base resin is used, a metal laminate such as described in JP2002-240193A publication or JP2002-245609A publication has been proposed. According to the proposals, there is described that the metal laminate improves a productivity and it is effective for cost reduction, because a wet etching rate of polyimide is fast. In these patent applications, however, there is not any clear description about an oxide film of metal, and there is a problem that according to circumstances, an etching rate of polyimide becomes slow and the so-called over-etching phenomenon is caused, which results in deterioration of a shape and reduction in productivity. Further, since many wet-etchable polyimides have an average thermal expansion coefficient of 25 ppm/° C. or more, a difference in thermal expansion coefficient between the wet-etchable polyimide and metal material such as stainless steel or the like is large and the polyimide is poor in warp or size stability, it is actually difficult to use such a polyimide as suspension material.